1. Field of the Invention
The present invention relates generally to an elastic bushing filled with a viscous fluid, and more particularly to such a fluid-filled elastic bushing which exhibits an excellent characteristic of damping input vibrations.
2. Discussion of the Prior Art
As one type of vibration insulator for flexible or elastic connection of a shaft member of a vibration system to a support structure, there is known a vibration-isolating bushing such as an elastic bushing which includes a tubular elastic body which is closed at its one end and open at the other end. For example, the tubular elastic body is secured to a suitable support member such as a frame of a front-engine front-drive vehicle having a strut type front suspension system, such that a shaft member such as a compression rod which serves as a pivot on the rear side of a L-type lower arm of the suspension system is fixedly inserted into the bore of the elastic body. According to this arrangement, the shaft member is connected to the support member in a vibration isolating or damping manner, so that the tubular elastic body restrains displacements of the shaft member in one of its opposite axial directions and in its radial direction.
The elastic bushing having the conventional construction employing a single formed rubber mass as the elastic body as described above is uncapable of providing a sufficient damping effect with respect to vibrations applied thereto. In particular, it has been difficult to provide the conventional elastic bushing with excellent damping characteristic to input vibrations which has a comparatively low frequency range.
Where the elastic bushing is used as a vibration-isolating bushing for flexibly connecting the compression rod of the L-type lower arm of the vehicle front suspension system to the vehicle frame,, the elastic body suffers from low vibration damping characteristic with respect to vibrations which are applied in the radial direction of the bushing, particularly where the frequency of the vibrations falls within a range of approximately 10-15 Hz, which is the resonance frequency of the suspension system. Hence, the elastic bushing is uncapable of effectively preventing shimmy vibrations of the vehicle in running, which have an adverse effect on the steering and running stabilities of the vehicle. Thus, the known elastic bushing has a problem that should be solved.